1. Field of the Invention
The present invention relates to a novel gas diffusion electrode. More particularly, it relates to a novel gas diffusion electrode which is suitable as an oxygen reduction electrode for an electrolysis of an alkali metal chloride or an electrode in an oxidizer side of a fuel cell.
2. Description of the Prior Arts
Recently, it has been proposed to use a gas diffusion electrode as a cathode for an electrolysis of an aqueous solution of an alkali metal chloride for producing an alkali metal hydroxide and chlorine and to feed an oxygen containing gas to the gas diffusion electrode. This type of electrolysis is carried out at remarkably low decompostion voltage without a generation of hydrogen gas from the cathode by following cathodic reaction: EQU H.sub.2 O+1/2O.sub.2 +2e.sup.- .fwdarw.2OH.sup.-
(U.S. Pat. Nos. 3,923,628 and 4,035,254). The electrode used in the electrolysis is a gas diffusion electrode having three phase zone to contact a gas, a liquid and a solid in the electrode to perform an cathodic reaction. The conventional gas diffusion electrode comprises a current collector and a catalyst containing porous layer formed by sintering a mixture of a catalyst for accelerating said reaction, said porous layer composed of a carrier for carrying said catalyst and a hydrophobic material for preventing permeation of an electrode and having a function as a binder. Thus, the conventional gas diffusion electrode does not have satisfactory characteristics to give a large overvoltage and to be unsatisfactory reproducibility. Moreover, when the electrode is used for a long period, loss of water repellency, crackings on the surface of the electrode and loss of a catalytic activity arise which lead to unsatisfactory durability.
On the other hand, the same disadvantages are found on an electrode in an oxidizer side of a fuel cell using an oxygen-containing gas as an oxidizing reagent. That is, the reaction occuring at the electrode is not satisfactorily fast and the performance of the cell is poor.
The inventors have studied to overcome these disadvantages of the conventional gas diffusion electrodes and have found that a perforating agent used for a preparation of a gas diffusion electrode highly improve the charactertistics of an electrode and these disadvantages of the conventional gas diffusion electrodes can be overcome by using a specific material as the perforating agent.